Acetone, butanol and ethanol, collectively referred to as ABE, are important raw materials in medicine, pesticide, plastic, rubber and light industry, and are also very important chemical solvents. Therefore, the study of ABE has a very important effect on the development of modern industry.
Acetone, also known as dimethylketone, is a colorless transparent liquid and highly volatile. Acetone is not only an important organic solvent but also an important chemical material, which can be used in explosive, plastic, fiber, leather, spray painting and other industries, and can also used for synthesizing ketene, acetic anhydride, iodoform, polydiene rubber, epoxy resin and the like.
Butanol, also known as 1-butanol, is a colorless transparent liquid with strong odor of alcohol. It is slightly soluble in water. The relative density is 0.81 and the boiling point is 117.7° C. It belongs to a second-stage flammable liquid. Butanol, an important organic materials and chemical solvents, is widely used in various kinds of plastic, rubber goods, resins, leather, papermaking and other light industries. Another important role of butanol is acting as a new biofuel with great potential nowadays, which is known as second-generation biofuels. Compared with ethanol, butanol has a higher combustion value, may support cars running more 30% journey, has similar properties to hydrocarbon, no modification is required for automobile cylinder, has low volatility, is non-hydrophilic and free from corrosion, has good high-octane rating and anti-detonating quality. Hence, under the situation that the fossil resources decrease gradually in the world, the research and development of butanol becomes a new hot topic rapidly.
3-hydroxy butanone, also known as acetoin or acetyl methyl carbinol, is usually light yellow liquid or crystal. It is naturally occurring in corn, grape, berries, cheese, meat and many other foods, and widely used as one of the spices. China's national standard GB2760-86 stipulates that it can be used as food-flavors, and the security number in Flavor and Extract Manufacturers Association (FEMA) is 2008. In addition, 3-hydroxy butanone can also serve as an important raw material in chemical synthesis. For example, it can be used for synthesizing a chiral smectic material and a nematic material.
Traditional chemical preparation of 3-hydroxy butanone is mainly chemical process or enzymatic conversion, the raw material is mainly diacetylbutanedione and 2,3-butanediol. In 1998, Martin Studer et al. from the British Witwatersrand University used modified platinum as a catalyst to selectively hydrogenate, thereby reducing diacetyl, the yield is 30%. Slipszenko from Hull University in British also developed platinum as a catalyst to hydrogenate, thereby reducing diacetyl to form 3-hydroxyl butanone, the yield is 85%. However, heterogeneous catalytic hydrogenation reaction is usually carried out under high pressure, so high quality facility is required and the catalyst used is expensive. In 1992, Hummel et al. from the United States obtained diacetyl reductase from lactobacillus or yeast by adopting microorganism culture methods, and then generated 3-hydroxy butanone under conditions of pH5, 70° C. by using the reductase and coenzyme NADH to catalyze diacetyl, the highest yield is up to 100%. RH Blom from the United States Department of Agriculture synthesized diacetyl and 3-hydroxy butanone from 2,3-butanediol by an oxidative dehydrogenation process in 1945. 2,3-butanediol together with air go through Pyrex tube reactor (copper shavings are filled thereinto) after heated under 140° C., the reaction temperature is 315° C., the products are diacetyl (the yield is 33%) and 3-hydroxy butanone (the yield is 25%). A. Hilmi from Poitiers University in France prepares 3-hydroxy-2-butanone by electrochemical oxidation method, the method is carried out in an electrolytic bath, wherein the diaphragm is an ion exchange membrane and the electrodes in reaction are all reversible hydrogen electrodes. Positive electrode is Pt—Pb, and porous Pt/Ir (10%) is as a counter electrode, the electrolyte is HClO4, the solvent is ultra-pure water, the reaction temperature is 40° C., and the battery voltage is 0.8V. Using this electrolytic oxidation method, the products include diacetyl and carbon dioxide besides 3-hydroxy butanone, the yield is 94%. However, there exist the problems of serious environment pollution and product quality as for the chemical method. Furthermore, the raw materials are mainly from non-renewable fossil resources, which limits the development in the long run.
In addition, 3-hydroxy butanone can also be produced by microbial fermentation. In most microorganisms, two molecules of pyruvic acid synthesize one molecule of acetolactate under the action of acetolactate synthetase, and then acetolactate under the action of acetolactate decarboxylase can form 3-hydroxy butanone. Acetolactate can also be naturally oxidative decarboxylated in the presence of oxygen to generate diacetyl, and then the diacetyl is reduced to generate 3-hydroxy butanone. However, 3-hydroxy butanone can be further reduced to generate 2,3-butanediol, the reaction of generating 3-hydroxy butanone by the reduction of diacetyl and the reaction of generating 2,3-butanediol by the reduction of 3-hydroxy butanone can be catalyzed by the same enzyme (2,3-butanediol dehydrogenase). Therefore, in many microorganisms, 3-hydroxy butanone is often as an intermediate product of 2,3-butanediol, accompanied by the generation of diacetyl, which affects the yield and separation. At present, it has been found that many strains can produce 3-hydroxy butanone, for example: Lactococcus lactis, Lactobacillus casei, Saccharomyces cerevisiae and other dairy products or wine fermentation strains, but the yield of 3-hydroxy butanone is less than 1 g/L. Klebsiella pneumonia, Enterobacter aerogenes, Bacillus subtilis and the like can also be fermented to produce 3-hydroxy butanone, and this methos has a high yield, but these strains are mainly used to produce 2,3-butanediol, 3-hydroxy butanone is only as by-product. Olson and Johnson convert 226 g/L glucose to 14 g/L 3-hydroxy butanone and 97 g/L 2,3-butanediol using Enterobacter aerogenes. Cuiqing M A et al. from Shandong University produce chiral 3-hydroxy butanone and 2,3-butanediol by using recombinant Escherichia coli which contains 2,3-butanediol dehydrogenase gene and NADH oxidase gene, the concentration of chiral 3-hydroxy butanone reaches 36 g/L. Chinese patent application CN101008019A discloses the application of Bacillus subtilis strain in the preparation of 3-hydroxy butanone, wherein glucose is the main raw material, this method comprises fermenting 50 L Bacillus subtilis SFA-H31 (CGMCC 1869) in fermentation tank for 52 h, the conversion rate reaches 48.26%, the fermentation yield of 3-hydroxy butanone reaches 55.67 g/L, and confirms that the strain does not produce the by-products diacetyl and 2,3-butanediol. However, Bacillus subtilis et al. generally are aerobic growth and fermentation, and because one glucose will generate two NADH during the process of converting to 3-hydroxy butanone, if it is only used for producing 3-hydroxy butanone, NADH will be wasted. Meanwhile, as 2,3-butanediol and 3-hydroxy butanone are in the upstream and downstream of the same branch, it is hard for conventional cogeneration to individually regulate metabolic flux of them and effectively use NADH.